The present application claims priority of Chinese patent application Serial No. 01109633.0, filed Mar. 14, 2001, the content of which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a heat pump system for air conditioning and, more particularly, to a heat pump system for air conditioning adaptable to cold regions.
2. Description of Related Art
A heat pump for air conditioning has been used widely in the world. It can meet the heating requirements in winter with less consumption of energy. Because of its characteristics of convenient application, high energy utilization efficiency, and no pollutant generation, the heat pump for air conditioning should be the preferred electrical heating unit. However, when the outside temperature is below xe2x88x925xc2x0 C., the heating capacity and reliability of the conventional heat pump for air conditioning will decrease greatly, thus it can not meet the heating requirements in cold regions in winter. There have been known many proposals for the operation of heat pump for air conditioning with high efficiency, stability and reliability. In the prior art, a supplementary electric heater has been added to the indoor water pipe to resolve the problem of insufficient heat capacity. As disclosed in xe2x80x9cDevelopment of Packaged Air Conditioner For Cold Regionxe2x80x9d written by N.Horiuchi. and published in the Journal of Refrigeration in Japan, Vol.72, No. 7, Issue No.837, 1997, with a frequency conversion system used for the heat pump system, the refrigerant circulation volume is increased by operating the compressor at high frequency under low temperature conditions and refrigerant liquid is injected simultaneously into the working chamber of the compressor to prevent the chamber from being overheated. Additionally, a technical solution is disclosed in xe2x80x9c Development of Burner for Room Air Conditionerxe2x80x9d published in the Mitsubishi Heavy INC. Disclosing Bulletin in Japan, Vol.35, No.2, 1998, wherein the low temperature performance of the heat pump is improved by using kerosene burner to heat the outside heat exchanger under low temperature conditions. For the above mentioned solutions, it is necessary to provide additional equipment for the heat pump, resulting in complication of the system, an increase in cost and lower energy utilization efficiency, so the problems in the prior have not been resolved substantially.
To solve above-mentioned problems in the prior art, an object of the present invention is to provide a heat pump system for air conditioning adaptable to cold regions, which is simple in structure, low cost, easy to manufacture and assemble and highly effective in energy utilization.
According to the present invention, a heat pump system for air conditioning adaptable to cold regions comprises a compressor, a condenser, a thermal expansion valve and an evaporator, wherein the outlet of the compressor is connected with the refrigerant inlet of the condenser; the refrigerant outlet of the condenser is connected with a liquid receiver which is also connected with the inlet of a filter; the outlet of the filter is connected with the inlet of a subcooler through an electromagnetic valve; the outlet of the subcooler is connected with the inlet of the thermal expansion valve; the outlet of the thermal expansion valve is connected with the refrigerant inlet of the evaporator; the refrigerant outlet of the evaporator is connected with the inlet of the compressor. Either water circulation system or air circulation system can be applied to perform the heat exchange in the condenser, and the heat absorbed by water or air is released in a fan coil unit. This structure features that said compressor is a scroll compressor which is provided with a supplementary inlet on the working chamber thereof; the inlet of an additional expansion valve is connected with the joint between said electromagnetic valve and the inlet of a subcooler; the outlet of the additional expansion valve is connected with the supplementary inlet of the subcooler; and the supplementary outlet of the subcooler is connected with the supplementary inlet of the compressor through a shut-off valve.
With the above-described connections in accordance with the present invention, and there is provided a supplementary pipe paralleled to the main pipe between the condenser and the compressor for adding evaporated refrigerant to the compressor, heat exchange occurs between the two parts of refrigerant within the main pipe and the refrigerant within the supplementary pipe in the subcooler. So sufficient evaporated refrigerant can be injected into the working chamber of the compressor through the main inlet and the supplementary inlet under low temperature conditions. Thus the low operating temperature range of the unit is widened. According to the present invention, the heat pump system for air conditioning can operate with stability and reliability at xe2x88x9215xc2x0 C. for a long term, further, the exhaust temperature is stable and does not go beyond the limit of 130xc2x0 C., thus it can meet the heating requirements in cold regions perfectly. By comparison with the prior art, the unit only has an addition of an expansion valve so almost no other component except the expansion valve causes the increase of the cost of the unit. As described above, the heat pump system for air conditioning is simple in structure, low cost, easy to manufacture and assemble and highly effective in energy utilization. Thus it is particularly suitable for popularization and application in cold regions.